1. Field of the Invention
The present invention relates generally to a method for forming cell arrays on a substrate to facilitate high-throughput diagnostic analysis of a plurality of cell samples and, in particular, to cell arrays in which the discrete cell samples are arranged substantially in a monolayer with positive and negative controls, as well as test samples, arranged on the same substrate. More particularly, the present invention relates to cell arrays comprising multiple test and control samples arranged on a single substrate upon which immunohistochemistry, fluorescent in situ hybridization, and cytogenetic analyses may be conducted.
2. Description of the Related Art
Clinical analysis of cell samples obtained from patient specimens are routinely conducted by medical personnel and are useful tools for diagnosing and treating various diseases and medical conditions. Techniques for conducting clinical analyses have become increasing sophisticated as advances in medicine have led to methods of early detection and diagnosis of diseases and medical conditions. Such sophisticated techniques include, for example, immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH), which can be useful for diagnosing diseases, such as cancer. Additionally, cytogenetic assays can be useful for diagnosing diseases and medical conditions associated with chromosomal aberrations, such as, for example, Down's syndrome.
As increasingly sophisticated techniques for detecting and diagnosing diseases and medical conditions have become routine, there is increased interest in simplified procedures for conducting these techniques that do not rely on the highly trained skills of medical personnel, thereby allowing the possibility of dramatically increasing the number of samples that can be analyzed at the same time. Traditionally, diagnostic assays such as IHC, FISH and cytogenetic assays are performed on a substrate, usually a glass microscope slide, containing one sample per slide. The single sample per slide may be either a patient sample or a control sample, which is analyzed in conjunction with the results of the patient sample to mitigate the risk of false positives. Typically, cell samples, whether they be control or patient samples, are applied to the microscope slide using a non-standardized drop method.
Unfortunately, the current state of the art methods for dispensing drops of cells onto microscope slides suffer from high variability due to the individual techniques employed by various operators. Typically, large drops in the range of 10-100 μL are dropped onto a slide and allowed to flow across the surface of the slide with the hope that a uniform distribution of the cells will result. In order to obtain optimum results, the environment in which the drops are applied to the slides must be carefully controlled with respect to temperature and humidity. However, these methods are considered more of an art than a science and frequently result in considerable overlap of cells and non-uniform dispersal of the cells across the surface of the substrate. Overlap and non-uniformity may lead to inefficient or insufficient interaction between a test reagent and a target, which may ultimately lead to poor detection and a misdiagnosis.
The diagnostic assays for use with the cell arrays contemplated herein typically involve the use of antibodies, enzymes, fluorophores, chromogens and other expensive reagents. Accordingly, it is advantageous to conduct the assay in as small a volume as possible to minimize costs. For example, a routine IHC assay requires a series of steps, including procuring cells from a biological sample, depositing the cells onto a substrate, and processing the cell sample so that it is ready to receive a test reagent or probe. The probe is generally incubated with the cell sample prior to removal of excess probe and addition of a detection reagent, such as an antibody, that recognizes the interaction between the probe and the protein of interest. Finally, an oil coating may be applied to the substrate to prevent evaporation and a cover slip added to the slide to facilitate image analysis, either through a microscope or an automated imaging system. A typical IHC assay conducted on a glass slide generally requires an area of about 25×50 mm, requires the use of between about 50-100 μL of reagent per assay, and requires multiple glass slides in order to process multiple samples.
The variability arising from the application of cell samples to the surface of the substrate may lead to increased variability in the results of the clinical assays and ultimately to inaccurate diagnoses. By contrast, a more ideal result is consistent application of cell samples (patient and control) to provide a uniform distribution of cells arranged substantially in a monolayer at a particular location on the substrate. An even more ideal result is the ability to miniaturize the process such that multiple samples can be included on the same substrate. In this way, for example, several patient samples can be subjected to the desired assay on the same slide as the control samples. An additional benefit of the miniaturization process is to decrease the quantity of sample and reagent needed to conduct the diagnostic assay, thereby decreasing the cost of the test while at the same time increasing the number of assays that can be performed with higher fidelity.